As a linear actuator in which a moving element is allowed to reciprocate with respect to a stator in one direction due to act of magnetism, many types of linear actuators have been conventionally known. Among them, a linear actuator having a configuration described in Patent Literature 1 described below is known.
This linear actuator is referred as an outer movable type in which a moving element is arranged outside a stator. In the linear actuator, the outer core as the moving element is disposed outside the inner core as the stator so that the outer core and the inner core are disposed on the same axial center. Further, permanent magnets are provided outside the inner core, and magnetic pole portions are provided inside the outer core. The permanent magnets are brought close on the magnetic pole portions with certain gaps formed therebetween, so that it is possible to electrically control and change a magnetic field formed between the permanent magnets and the magnetic pole portions. Accordingly, the outer core is allowed to reciprocate in a direction of the axial center.
A configuration of the linear actuator is specifically described. The inner core is supported, in a radial direction of the shaft, by a shaft passing through a through hole formed in the axial center of the inner core, and a pair of flat springs is provided at an outer circumference of the shaft so as to interpose the inner core in front and rear of the inner core. Further, the outer core is elastically supported with respect to the axial direction of the shaft by being connected from front and rear surfaces by the pair of flat springs. The flat springs are formed in an “8” shape when viewed in the axial direction of the shaft, and through holes are formed in crossing portions at centers of the flat springs. Thus, by simultaneously inserting the shaft into the through holes and through holes formed in the inner core, the inner core and the flat springs can be coaxially arranged, and the outer core connected to the flat springs, similarly to the inner core, can be coaxially arranged.
Moreover, a large diameter portion not being able to pass through the through hole is formed at a side of one end of the shaft, and a male screw is formed at a side of the other end. As described above, by screwing a nut to the screw after inserted into the through holes of the flat springs and the inner core, it is possible to fix positions of the flat springs and the inner core to the shaft.
In such a linear actuator, predetermined gaps are maintained while allowing the permanent magnets and the magnetic pole portions to appropriately face each other. This is important to maintain characteristics of the linear actuator. To achieve this, various techniques for restricting positional relation between the inner core and the outer core have been suggested.
For example, in the above-described Patent Literature 1, a groove is formed at an outer circumference of the flat spring, and an axial portion is formed at the outer core. By engaging the groove with the axial portion, a positional relation between the flat spring and the outer core is restricted, and a positional relation between the outer core and the inner core is indirectly restricted.
In addition, in Patent Literature 2, the shaft is formed in a polygonal shape, and the through holes of the inner core and the flat springs are formed in a polygonal shape to correspond to the shape of the shaft. Thus, via the shaft, a positional deviation in a circumferential direction between the inner core and the flat spring is suppressed. Accordingly, a positional relation between the inner core and the outer core is indirectly restricted.
Moreover, in Patent Literature 3, when there is a relative displacement in a radial direction between the inner core and the outer core, abutting portions which abut before the permanent magnets abut the magnetic pole portions and function as a stopper are formed between the inner core and the outer core. The positional relation between the inner core and the outer core in operation is also restricted by the abutting portions.